Cryo-EM structure of oxysterol-bound human Smoothened coupled to a heterotrimeric Gi

Xiaofeng Qi, Heng Liu, Bonne Thompson, Jeffrey McDonald, Cheng Zhang () and Xiaochun Li ()
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Xiaofeng Qi: University of Texas Southwestern Medical Center
Heng Liu: University of Pittsburgh, School of Medicine
Bonne Thompson: University of Texas Southwestern Medical Center
Jeffrey McDonald: University of Texas Southwestern Medical Center
Cheng Zhang: University of Pittsburgh, School of Medicine
Xiaochun Li: University of Texas Southwestern Medical Center

Nature, 2019, vol. 571, issue 7764, 279-283

Abstract: Abstract The oncoprotein Smoothened (SMO), a G-protein-coupled receptor (GPCR) of the Frizzled-class (class-F), transduces the Hedgehog signal from the tumour suppressor Patched-1 (PTCH1) to the glioma-associated-oncogene (GLI) transcription factors, which activates the Hedgehog signalling pathway1,2. It has remained unknown how PTCH1 modulates SMO, how SMO is stimulated to form a complex with heterotrimeric G proteins and whether G-protein coupling contributes to the activation of GLI proteins3. Here we show that 24,25-epoxycholesterol, which we identify as an endogenous ligand of PTCH1, can stimulate Hedgehog signalling in cells and can trigger G-protein signalling via human SMO in vitro. We present a cryo-electron microscopy structure of human SMO bound to 24(S),25-epoxycholesterol and coupled to a heterotrimeric Gi protein. The structure reveals a ligand-binding site for 24(S),25-epoxycholesterol in the 7-transmembrane region, as well as a Gi-coupled activation mechanism of human SMO. Notably, the Gi protein presents a different arrangement from that of class-A GPCR–Gi complexes. Our work provides molecular insights into Hedgehog signal transduction and the activation of a class-F GPCR.

Date: 2019
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DOI: 10.1038/s41586-019-1286-0

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